[PATCH 01/14] fs: Support THPs in vfs_dedupe_file_range

Matthew Wilcox (Oracle)
2020-10-14T09:21:48Z

We may get tail pages returned from vfs_dedupe_get_page(). If we do,
we have to call page_mapping() instead of dereferencing page->mapping
directly. We may also deadlock trying to lock the page twice if they're
subpages of the same THP, so compare the head pages instead.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
fs/read_write.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 19f5c4bf75aa..ead675fef582 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1604,6 +1604,8 @@ static struct page *vfs_dedupe_get_page(struct inode *inode, loff_t offset)
*/
static void vfs_lock_two_pages(struct page *page1, struct page *page2)
{
+ page1 = thp_head(page1);
+ page2 = thp_head(page2);
/* Always lock in order of increasing index. */
if (page1->index > page2->index)
swap(page1, page2);
@@ -1616,6 +1618,8 @@ static void vfs_lock_two_pages(struct page *page1, struct page *page2)
/* Unlock two pages, being careful not to unlock the same page twice. */
static void vfs_unlock_two_pages(struct page *page1, struct page *page2)
{
+ page1 = thp_head(page1);
+ page2 = thp_head(page2);
unlock_page(page1);
if (page1 != page2)
unlock_page(page2);
@@ -1670,8 +1674,8 @@ static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
* someone is invalidating pages on us and we lose.
*/
if (!PageUptodate(src_page) || !PageUptodate(dest_page) ||
- src_page->mapping != src->i_mapping ||
- dest_page->mapping != dest->i_mapping) {
+ page_mapping(src_page) != src->i_mapping ||
+ page_mapping(dest_page) != dest->i_mapping) {
same = false;
goto unlock;
}
--
2.28.0